American Mink
From Wikipedia, the free encyclopedia The American mink (Neovison vison) is a semi-aquatic species of Mustelid native to North America, though human intervention has expanded its range to many parts of Europe and South America. Because of this, it is classed as Least Concern by the IUCN.[[|1]] Since the extinction of the sea mink, the American mink is the only extant member of the genus Neovison. The American mink is a carnivore which feeds on rodents, fish, crustaceans, frogs and birds. In its introduced range in Europe, the American mink has been linked to declines in European mink and water vole. It is the most frequently farmed animal for its fur, outdoing in economic importance the silver fox, sable, marten and skunk.[[|3]] Evolution As a species, the American mink represents a more specialised form than the European mink in the direction of carnivory, as indicated by the more developed structure of the skull.[[|5]] Fossil records of the American mink go back as far as the Irvingtonian, though the species is uncommon among Pleistocene animals. The fossil range of the American mink corresponds with the species' current natural range. The American minks of the Pleistocene did not differ much in size or morphology from modern populations, though a slight trend toward increased size is apparent from the Irvingtonian through to the Illinoian and Wisconsinan periods.[[|6]] Although superficially similar to the European mink, studies indicate that the American mink's closest relative is the kolonok of Asia. The American mink has been recorded to hybridize with European minks and polecats in captivity, though the hybrid embryos of the American and European minks are usually reabsorbed.[[|7]] edit] Subspecies As of 2005[update],[[|8]] 15 subspecies are recognised. edit] Physical description edit] Build [[|]] Enlarge Skeleton of an American mink from the Muséum national d'histoire naturelle [[|]] Enlarge Skull as illustrated in Coues' A monograph of North American Mustelidae The American mink differs from members of the genus Mustela (stoats and weasels) by its larger size and stouter form, which closely approaches that of martens. It shares with martens a uniformly enlarged, bushy and somewhat tapering tail, rather than a slenderly terete tail with an enlarged bushy tip, as is the case in stoats.[[|10]] The American mink is similar in build to the European mink, but the tail is longer (constituting 38-51% of its body length).[[|11]] The American mink has a long body, which allows the species to enter the burrows of prey. Its streamlined shape helps it to reduce water resistance whilst swimming.[[|12]] The skull of the American mink is similar to that of the European mink, but is more massive, narrower and less elongated, with more strongly developed projections and a wider, shorter cranium. The upper molars are larger and more massive than those of the European mink.[[|13]] The dental formula is: Domestic mink, which are bred in fur farms, have 19.6% smaller brains, 8.1% smaller hearts, and 28.2% smaller spleens than wild mink.1415 The feet are broad, with webbed digits.10 It generally has eight nipples, with one pair of inguinal teats and three pairs of abdominal teats.11 The adult male's penis is 2.2 inches (5.6 cm) long, and is covered by a sheath. The baculum is well developed, being triangular in cross section and curved at the tip.12 Males measure 13–18 inches (34–45 cm) in body length, while females measure 12–15 inches (31–37.5 cm). The tail measures 6–10 inches (15.6–24.7 cm) in males and 6–8 inches (14.8–21.5 cm) in females. Weight varies with sex and season, with males being heavier than females. In winter, males weigh 1–3 pounds (500–1,580 g) and females 1–2 pounds (400–780 g) Maximum heaviness occurs in autumn.5 American mink paws, as illustrated by Ernest Thompson Seton edit Fur The American mink's winter fur is denser, longer, softer and more close-fitting than that of the European mink. The winter fur's tone is generally very dark blackish-tawny to light-tawny. Colour is evenly distributed over all the body, with the lower side being only slightly lighter than the upper body. The guard hairs are bright, dark-tawny, often approaching black on the spine. The underfur on the back is very wavy, greyish-tawny with a bluish tint. The tail is darker than the trunk and sometimes becomes pure black on the tip. The chin and lower lip are white. Captive individuals tend to develop irregular white patches on the lower surface of the body, though escaped individuals from Tartaria gradually lost these patches. The summer fur is generally shorter, sparser and duller than the winter fur.11 The thick underfur and oily guard hairs render the pelage water resistant, with the length of the guard hairs being intermediate between those of otters and polecats, thus indicating that the American mink is incompletely adapted to an aquatic life. It moults twice a year, during spring and autumn.12 It does not turn white in winter.16 A variety of different colour mutations have arisen from experimental breeding on fur farms.7 edit Locomotion On land, the American mink moves by a bounding gait, with speeds of up to 6.5 kilometres per hour (4.0 mph). It also climbs trees and swims well.17 During swimming, the mink propels itself primarily through undulating movements of the trunk. When diving, the American mink undergoes a state of rapid bradycardia, which is likely an adaptation to conserving oxygen.12 In warm water (24 °C (75 °F)), the American mink can swim for three hours without stopping, while in cold water it can die within 27 minutes.18 It generally dives to depths of 12 inches (30 cm) for 10 seconds, though depths of three metres lasting 60 seconds have been recorded. It typically catches fish after 5-20 second chases.17 edit Senses and scent glands The American mink relies heavily on sight when foraging. Its eyesight is clearer on land than underwater. Its auditory perception is high enough to detect the ultrasonic vocalisations (1-16 kHz) of rodent prey. Its sense of smell is comparatively weak. The American mink has two anal glands, which are used for scent marking, either through defecation or by rubbing the anal region on the ground. The secretions of the anal glands are composed of 2,2-dimethylthietane, 2-ethylthietane, cyclic disulfide, 3,3-dimethyl-1,2-dithiacyclopentane, and indole. When stressed, the American mink can expel the contents of its anal glands at a distance of 12 inches (30 cm).12 Scent glands may also be located on the throat and chest.19 The smell produced by these scent glands was described by Clinton Hart Merriam as more unbearable than that produced by skunks, and added that it was "one of the few substances, of animal, vegetable, or mineral origin, that has, on land or sea, rendered me aware of the existence of the abominable sensation called nausea".20 edit Behaviour edit Social and territorial behaviours A southern mink (Neovison v. vulgivagus) in a threatening posture American mink in burrow American mink territories are held by individual animals with minimal intrasexual overlap, but with extensive overlap between animals of the opposite sex. Most territories are located in undisturbed rocky coastal habitats with broad littoral zones and dense cover. They may also occur on estuaries, rivers and canals near urban areas. Home ranges are typically 1–6 kilometres (0.62–3.7 miles) long, with male territories being larger than those of females.17 As long as it is close to water, the American mink is not fussy over its choice of den. Mink dens typically consist of long burrows in river banks, holes under logs, tree stumps or roots and hollow trees, though dens located in rock crevices, drains and nooks under stone piles and bridges are occasionally selected. Burrows dug by American minks themselves are typically about four inches in diameter and may continue along for 10–12 feet (300–370 cm) at a depth of 2–3 feet (61–91 cm). The American mink may nest in burrows dug previously by muskrats, badgers and skunks, and may also dig dens in old ant hills. The nesting chamber is located at the end of a four-inch tunnel, and is about a foot in diameter. It is warm, dry and lined with straw and feathers.21 The American mink's dens are characterized by a large number of entrances and twisting passages. The number of exits vary from 1-8.18 The American mink normally only vocalises during close encounters with other minks or predators. Sounds emitted by the American mink include piercing shrieks and hisses when threatened and muffled chuckling sounds when mating. Kits squeak repeatedly when separated from their mothers.19 Ernest Thompson Seton reported hearing minks growl and snarl when confronting a threat.22 During aggressive interactions, the American mink asserts its dominance by arching its back, puffing up and lashing its tail, stamps and scrapes the ground with its feet and opens its mouth in a threat-gape. Should this be unsuccessful, fights may result, with injuries to the head and neck.19 edit Reproduction and development American mink kits The American mink is a promiscuous animal, which does not form pair-bonds.17 The mating season for American minks begins from February in its southern range to April in the north.12 In its introduced range, the American mink breeds one month earlier than the European mink.23 Males commonly fight during the mating season, which may result in the formation of loose, temporary dominance hierarchies governing access to receptive females.17 The mating season lasts for three weeks, with ovulation being induced by the presence of males. The mating process in the American mink is violent, with the male typically biting the female on the nape of the neck and pinning her with his forefeet. Mating lasts from 10 minutes to four hours. Females are receptive for 7-10 day intervals during the three week breeding season, and can mate with multiple males. Along with the striped skunk, the American mink is among the only mammals to mate in spring whilst possessing a short delay before the occurrence of implantation. This delayed implantation allows pregnant minks to keep track of environmental conditions and select an ideal time and place for parturition.12 The gestation period lasts from 40–75 days, with actual embryonic development taking place after 30–32 days, thus indicating that delayed implantation can last from 8–45 days. The young are born either in April or June, with litters consisting of four kits on average.12 Exceptionally large litters of 11 kits have been recorded in Tartaria and 16 in the United States.23 The kits are blind at birth, weighing six grams and possessing a short coat of fine, silver-white hairs.12 The kits are dependent on their mother's milk, which contains 3.8% lipids, 6.2% protein, 4.6% sugar and 10.66% mineral salts.23 Their eyes open after 25 days, with weaning occurring after five weeks. The kits begin hunting after eight weeks of age, but stay close to their mother until autumn, when they become independent. Sexual maturity is attained during the kit's first spring, when they are about 10 months old.12 edit Diet American mink with fish, in Norway American mink with a salmon The American mink is a carnivorous animal, which feeds on rodents, fish, crustaceans, amphibians and birds. It kills vertebrate prey by biting the back of the head or neck, leaving canine puncture marks 9–11 mm apart.24 In its natural range, fish are the American mink's primary prey. Although inferior to the North American river otter in hunting fish, Audubon and Bachman once reported seeing a mink carrying a foot-long trout. Mink inhabiting the prairie sloughs primarily target frogs, tadpoles, mice.25 It is a formidable predator of muskrats, which are chased underwater and killed in their own burrows. Among the rodents killed by the American mink in its native range are rats and mice of the genus Hesperomys, Microtus, Sigmodon and Neotoma. Marsh rabbits are frequently taken in marshy or swampy tracts.26 In Tartaria, the American mink's most important food items are voles, fish, crustaceans, frogs and aquatic insects. In winter, aquatic foods predominate, while land-based prey increases in importance during the spring. Within the Altai Mountains, the American mink feeds predominantly on mammals such as rodents, shrews and moles, as well as birds, reptiles, amphibians and fish. Among the 11 different bird species preyed upon by minks in Altai are dippers and pine grosbeaks. Among fish, small species predominate in the diet of minks in Altai, and include ; minnows, gudgeons and wide-headed sculpins. In the Sverdlovsk and Irkutsk Oblasts, mouse-like rodents are the American mink's most important foods, followed by birds, fish and insects. In the Russian Far East, where crustaceans are scarce, the American mink feeds extensively on amphipods.27 In the British Isles, dietary composition varies seasonally and regionally. European rabbits are the most commonly taken prey in areas where they are common, especially in summer. A range of small rodents and insectivores are preyed upon, but to a lesser degree. European hares are occasionally attacked. Minks in Britain prey on several bird species, with ducks, moorhens and coots being most frequently targeted on lakes and rivers, while gulls are taken in coastal habitats. Aquatic species preyed upon in Britain include European eels, rock-pool fish such as blenny, shore crabs and crayfish.28 American Mink have been implicated in the decline of the water vole in the United Kingdom and linked to the decline of water fowl across their range in Europe. They are now considered vermin in much of Europe and are hunted for the purpose of wildlife management.29 In the Cape Horn Biosphere Reserve, mammals, including both native and exotic rodents, are the American mink's main prey throughout the year, though birds are of equal importance during their summer nesting period.30 The American mink may pose a threat to poultry. According to Clinton Hart Merriam31 and Ernest Thompson Seton,32 although the American mink is a potential poultry thief, it is overall less damaging than the stoat. Unlike the stoat, which often engages in surplus killing, the mink usually limits itself to killing and eating one fowl during each attack. Studies in Britain indicate that poultry and game birds only constitute 1% of the animal's overall diet.28 edit Relationships with other predators The American mink replaces and sometimes kills the European mink wherever their ranges overlap.33 The decline of European mink populations seems to coincide with the spread of the American mink.34 The diets of the American mink and European otter overlap to a great extent. In areas where the two species are sympatric, competition with the otter for fish causes the American mink to hunt land-based prey more frequently.35 edit Intelligence An early behavioral study was performed in the 1960s that assessed visual learning ability in mink, ferrets, skunks, and house cats. Animals were tested on their ability to recognize objects, learn their valences and make object selections from memory. Mink were found to outperform ferrets, skunks and cats in this task, however this letter (short paper) fails to account for a possible conflation of a cognitive ability (decision making, associative learning) with a largely perceptual ability (invariant object recognition).36 edit Range edit Natural The species' natural range encompasses North America from Alaska and Canada through the United States except Arizona and the more arid areas of California, Nevada, Utah, New Mexico, and western Texas.1 edit Introduced edit Mainland Europe and British Isles An American mink being released from a fur farm in Rome by a member of the ALF It is thought that feral American minks in Europe are of domesticated stock derived from the vison, melampeplus and ingens subspecies. The first specimens were imported to Europe in 1920 for fur-farming purposes. The American mink was introduced in Italy in the 1950s, and currently resides mostly in the northeastern part of the Italian Peninsula. The majority of these populations do not appear to be self-sufficient, though minks in the Monti Prenestini and Simbruini in Lazio have reproduced successfully.37 The first mink farm in Norway was built in 1927, with escapees establishing wild populations within 30 years of its establishment. The first feral mink populations arose in 1930, establishing territories in southwestern Norway. These feral minks, augmented by further escapees, formed the basis of a strong population in Hordaland by the end of World War II. Feral mink colonised eastern Norway in 1930 and had become established in mosrt southeastern counties in the early 1940s. By 1950, feral mink reached central Norway, with further populations occurring in the northern counties of Nordland and Troms. During the post-World War II period up until 1965, mink had colonised most of the country. In modern times, the American mink occupies all of the Norwegian mainland, but is absent on some islands.38 The American mink was first imported to Great Britain in 1929, though a series of escapes and releases lead to the establishment of a self-sufficient feral population in Devon by the late 1950s, and others by the early 1960s. In Ireland, the American mink was not farmed until the early 1950s, thus feral populations established themselves there much later. The species is now widespread in mainland Great Britain and Ireland, though some places remain uncolonised. It has established itself on a few islands, including Arran, Lewis and Harris.17 The total mink population in Great Britain is estimated at 110,000 (England; 46,750, Scotland; 52,250, Wales; 9750). This population may be declining as European otter numbers increase. There are no estimates for the mink population in Ireland, but it is thought to be low, because of Ireland's strong otter population.39 edit Former USSR An American mink in Lithuania's Kėdainiai district In 1933, American minks were released into the Voronezh Oblast in European Russia. Until 1963, more minks were introduced in various quantities in the Voronezh and Arkhangelsk Oblasts, Karelia, in Kalininsk, Gorkovsk, Volgograd and Chelyabinsk Oblasts, and into Tatarstan and Bashkir, as well as the Lithuanian and Byelorussian SSRs. Beyond the Urals, American minks were introduced in the Sverdlovsk, Tyumen, Omsk, Kemerovo, Novosibirsk, Chita and Irkutsk Oblasts, in the Altai and Krasnoyarsk Krai, in the Tuvan, Buryat and Yakut Autonomous Soviet Socialist Republics, into the Magadan, Kamchatka and Amur Oblasts, into the Khabarovsk and Primorsky Krai, into the Chukotka Autonomous Okrug and several other locations, including Sakhalin and Urup Island. In the Caucasus, American mink were released into North Ossetia and Tien Shan. Originally, captive-bred mink were used, but wild specimens were later released in order to facilitate the species' acclimatisation within Soviet territories. Several years after the first release, introductions into the ranges already held by native European minks were discontinued, with most releases from then on taking place in Siberia and the Far East. Although considerable areas were occupied by the American mink by the early 1960s, the species' Soviet range was never continuous, as most released populations were isolated from one another.40 edit Iceland The species has been present in Iceland since the 1930s, and has become well established, despite it being heavily hunted since 1939. However, its population underwent a 42% decline during the years 2002-2006, which coincided with a decline in sandeel populations resulting in a drop in the seabird populations which the minks feed upon.41 edit South America The American mink was deliberately introduced for commercial fur production in several provinces of Patagonia in 1930. The animals escaped or were released from farms in Chubut Province and now occur in the Chubut and Río Negro Provinces and Tierra del Fuego.42 edit Diseases and parasites The American mink often carries light tick and flea infestations. Tick species known to infest minks include Ixodes hexagonus, I. canisuga, I. ricinus and I. acuminatus. Flea species known to infest minks include Palaeopsylla minor, Malaraeus penicilliger, Ctenopthalmus noblis, Megabothris walkeri, Typhloceras poppei and Nosopsyllus fasciatus. Endoparasites include Skrjabingylus nasicola and Troglotrema acutum.39 Transmissible mink encephalopathy (TME) is a prion disease of mink, similar to BSE in cattle and scrapie in sheep. A 1985 outbreak of TME in Stetsonville, Wisconsin resulted in a 60% mortality rate for the mink.43 Further testing revealed that this agent is transmissible between mink, cattle and sheep. The Stetsonville outbreak may have been due to the animals being fed the carcasses of other infected animals.44 edit Decline of wild mink Because of numerous incidents of domestic mink escaping from fur farms and establishing themselves in the wild, concern has arisen among conservationists of the possible repercussions such escapes may have on natural wild mink populations. Domestic mink are larger than wild mink, which may cause problems with the ecosystem when they escape. Mink are solitary, territorial animals and are intolerant of other mink. In times of overpopulation, mink control their own numbers by either killing each other through direct conflict or by causing weaker mink to be driven from territory until starvation sets in.45 When hundreds or thousands of released domestic mink flood an ecosystem, it causes a great disturbance for the wild mink, resulting in the deaths of the majority of the released mink and many of the wild mink from starvation or injuries incurred fighting over territory.45 When a domestic mink survives long enough to reproduce, it may cause problems for the wild mink populations.46 The adding of weaker domestic mink genes into wild mink populations is believed by some to have contributed to the decline of mink populations in Canada.46 A 2006 study in Denmark concluded that, due to frequent escapes from existing mink farms, “Closing mink farms may result in a crash of the free-ranging population, or alternatively it may result in the establishment of a better-adapted, truly feral population that may ultimately outnumber the population that was present before farm closures.” The study reported that more information would be necessary to determine the outcome.47 Another Danish study reported that a significant majority of the “wild” mink were mink which had escaped from fur farms. 47% had escaped within two months, 31% had escaped prior to 2 months, and 21% “may or may not have been born in nature.” The survival rate for recently released mink is reportedly lower than for wild mink, but if feral mink survive at least two months, their survival rate is the same as for wild mink. The authors suggest that this is due to the rapid behavioural adaptation of the animals.48 edit Relationships with humans edit Fur use American mink are primarily used in manufacturing ladies' fur coats, jackets and capes. Pelts which are not able to be converted into these items are made into trimming for cloth and fur coats. Mink scarves and stoles are also manufactured. Jackets and capes are mostly made from small to medium-sized specimens, usually females and young males, while trimming, scarves and stoles are made from adult males.49 The most valuable peltries come from eastern Canada which, although the smallest, are the silkiest and darkest.50 edit Trapping Illustration of an American mink approaching a board or log trap Although difficult to catch, the American mink, prior to being commercially farmed, was among the most frequently trapped furbearers as, unlike other furbearing mammals, it did not hibernate in winter, and could thus be caught on a nightly basis even in the far north.51 Minks were legally trapped from early November to early April, when their pelts were prime.52 Minks caught in traps cling to life with great tenacity, having been known to break their teeth in trying to extricate themselves from steel traps.53 Elliott Coues described a trapped mink as thus ; One who has not taken a Mink in a steel trap can scarcely form an idea of the terrible expression the animal's face assumes as the captor approaches. It has always struck me as the most nearly diabolical of anything in animal physiognomy. A sullen stare from the crouched, motionless form gives way to a new look of surprise and fear, accompanied with the most violent contortions of the body, with renewed champing of the iron till breathless, with heaving flanks, and open mouth dribbling saliva, the animal settles again, and watches with a look of concentrated hatred, mingled with impotent rage and frightful despair. The countenance of the Mink, its broad, low head, short ears, small eyes, piggish snout, and formidable teeth, is always expressive of the lower and more brutal passions, all of which are intensified at such times. As may well be supposed, the creature must not be incautiously dealt with when in a such a frame of mind. —53 One Native American method involved using a bait (usually a slit open chicken carcass filled with fish oil and oysters) tied to a rope and dragged around an area laden with traps. A mink would thus follow the trail into one of the traps. Another indigenous method involved placing traps scented with muskrat and female mink musk on top of disused muskrat dens by water-bodies. Attracted by the scent of food and a female, the mink would get caught in the trap and drown.54 On the American prairies, only the steel trap was used, because of the lack of timber.55 edit Farming Various American mink colour mutations Breeding American mink for their fur began in the late 19th century, as increasing enthusiasm for mink pelts made the harvesting of wild mink insufficient to meet the new demands. American mink are easily kept in captivity, and breed readily.56 In 2005, the U.S. ranked fourth in production behind Denmark, China and the Netherlands. Mink typically breed in March, and give birth to their litters in May. Farmers vaccinate the young kits for botulism, distemper, enteritis, and, if needed, pneumonia. They are harvested in late November and December. Methods for killing animals on fur farms, as on all farms, are detailed in the American Veterinary Medical Association's Report on Euthanasia which is used as a voluntary guideline for state departments of agriculture which have jurisdiction over all farms raising domesticated livestock, including mink.57 In the past, some mink-farms successfully provided pools of water for the mink to swim in,58 however, this practice is unheard of in modern mink production. Mink are motivated to access swimming water, and the absence of water is a source of frustration on modern farms.59 The ideal diet for farm-bred minks consists of 4-5 ounces of horse meat and a quarter pint of milk once daily.58 edit Colour mutations Selective breeding has produced a number of different colour shades in mink peltries, ranging from pure white, through beiges and browns and greys, to a brown that is almost black. The two standard strains are brown and "Black cross" which, when paired, produce numerous colour variations. When an albino mink is born, it is standard procedure in fur farms to breed it to other colour mutations in order to produce grey and light brown pastel shades. The following graph is a simplification of the main colour strains;60 edit As pets Mink as pet Wild mink can be tamed if caught young, but can be treacherous, and are usually not handled bare-handed.61 In the late 19th century, tame American minks were often reared for ratting, much as ferrets were used in Europe. They are more effective ratters than terriers, as they can enter rat-holes and drive rats from their hiding places. Because of their fondness for bathing, captive American minks may enter kettles or other open water-containing vessels. When minks of wild stock are confined with tame ones, the latter invariably dominate the former. They have also been known to dominate cats in confrontations.62 Though intelligent, mink are not quick to learn tricks taught to them by their owners.63 Even though domestic mink have been bred in captivity for almost a century, they have not been bred to be tame. Domestic mink have been bred for size, fur quality, and color. However, the US Fur Commission claims that "mink are truly domesticated animals" based on the number of years they have been kept on fur farms.64 edit Literature As an invasive species in the United Kingdom, mink have been the subject of at least two novels. Ewan Clarkson's 1968 Break for Freedom (published as Syla, the Mink in the USA) tells the story of a female mink escaped from a fur farm in a realistic style. On the other hand, A.R. Lloyd's 1982 Kine is a heroic fantasy with the mink as villains and weasels and other indigenous animals as heroes.